Campbell CS805 Manual de usuario

INSTRUCTION MANUAL

CS805 Heated-Needle

Anemometer

6/02

Campbell Scientific, Inc.

Warranty and Assistance

The CS805 HEATED-NEEDLE ANEMOMETER is warranted by

CAMPBELL SCIENTIFIC, INC. to be free from defects in materials and

workmanship under normal use and service for twelve (12) months from date of

shipment unless specified otherwise. Batteries have no warranty. CAMPBELL

SCIENTIFIC, INC.'s obligation under this warranty is limited to repairing or

replacing (at CAMPBELL SCIENTIFIC, INC.'s option) defective products.

The customer shall assume all costs of removing, reinstalling, and shipping

defective products to CAMPBELL SCIENTIFIC, INC. CAMPBELL

SCIENTIFIC, INC. will return such products by surface carrier prepaid. This

warranty shall not apply to any CAMPBELL SCIENTIFIC, INC. products

which have been subjected to modification, misuse, neglect, accidents of

nature, or shipping damage. This warranty is in lieu of all other warranties,

expressed or implied, including warranties of merchantability or fitness for a

particular purpose. CAMPBELL SCIENTIFIC, INC. is not liable for special,

indirect, incidental, or consequential damages.

Products may not be returned without prior authorization. The following

contact information is for US and International customers residing in countries

served by Campbell Scientific, Inc. directly. Affiliate companies handle repairs

for customers within their territories. Please visit www.campbellsci.com to

determine which Campbell Scientific company serves your country. To obtain

a Returned Materials Authorization (RMA), contact CAMPBELL

SCIENTIFIC, INC., phone (435) 753-2342. After an applications engineer

determines the nature of the problem, an RMA number will be issued. Please

write this number clearly on the outside of the shipping container.

CAMPBELL SCIENTIFIC's shipping address is:

CAMPBELL SCIENTIFIC, INC.

RMA#_____

815 West 1800 North

Logan, Utah 84321-1784

CAMPBELL SCIENTIFIC, INC. does not accept collect calls.

CS805 Table of Contents

PDF viewers note: These page numbers refer to the printed version of this document. Use

the Adobe Acrobat® bookmarks tab for links to specific sections.

1. General Description....................................................1

2. Specifications .............................................................1

3. Calibration and System Accuracy.............................2

3.1 Angular Sensitivity....................................................................................2

3.2 Pressure Change with Elevation................................................................3

3.3 Coupled Error of CE805...........................................................................3

4. Calibration...................................................................4

5. Installation...................................................................4

6. Wiring ..........................................................................6

7. Example Programs .....................................................7

Appendix

A. Secondary Error Considerations ..........................A-1

A.1 Pressure Validation..............................................................................A-1

A.2 Conductive Heat Transport across the Boundary Layer.......................A-1

A.3 Reference.............................................................................................A-3

Figures

1. Angular Response of CS805.......................................................................2

2. Pressure and Elevation................................................................................3

3. Plane of Calibrated Sensitivity....................................................................5

4. CS805, Sensor and Wiring Figure ..............................................................6

A-1. Changes in Kair with Temperature and Humidity................................A-2

This is a blank page.

CS805 Heated-Needle Anemometer

1. General Description

The CS805 Heated-Needle Anemometer is a dual-needle sensor containing a

heater element and two type T (copper-constantan) thermocouples. The -L

option on the model CS805-L indicates that the cable length is user specified.

This manual refers to the sensor as the CS805 and applies to the CS805-L as

well. The CS805 is meant for use with a current source, such as the CE805,

and a data acquisition system, such as the CR500, CR510, CR10(X), 21X,

CR23X, CR7, CR9000, and CR5000 dataloggers, all available from Campbell

Scientific. The CE805 is a four-channel current excitation device, outputting

31.1 milliamps across a maximum of 9.0 volts, used to power the CS805.

The CS805 measures wind speeds in low-flow applications. Its small size and

lack of moving parts makes it superior to cup, propeller, and sonic

anemometers in space-constrained environments. The CS805 uses stainless

steel hypodermic tubing to add durability to and resist corrosion of the

measurement circuitry. The interface of the needles and cable are

mechanically supported and chemically protected within a potting compound

forming the base of the probe.

The CS805 works on the principle of fluid heat transport from a cylinder. A

heater element is located in the tip of the long needle. The temperature

difference between the two needles is referenced to an external air temperature

measurement. Measuring the change of the temperature difference between the

two needles makes it possible to calculate wind speed.

2. Specifications

CS805

Specified Range: 5-500 cm/s (0.1-11 mph)

Calibrated Range: 5-500 cm/s

Precision Over Calibrated Range: 0.5 cm/s (0.01 mph)

Accuracy Over Calibrated Range: ±5 cm/s (±0.1 mph) or 5% of reading

Operating Temperature: -20 to 50°C

Storage Temperature: -20 to 50°C

Total Probe Length: 10.5 cm (4 in)

Probe Base Diameter: 0.95 cm (0.375 in)

Needle Length:

Long: 5 cm (2 in)

Short: 2 cm (0.8 in)

Needle Diameter: 1 mm (0.025 in)

Power Consumption: ~100 mW @ 31.1 mA

Heater Resistance: 101-102.5 Ohms

Thermocouple: Type T (Copper-Constantan)

Settling Time After Power is Switched On: 15 seconds

Cable Properties: See Belden Inc., cable number 8723

CE805

Channels: 4

Supply Current: 31.1 mA

Current Accuracy: ±2%

Maximum Voltage Output: 9 Volts

Power Consumption:

~25 mA plus 31.1 mA per channel being used

~150 mA when all 4 channels are used

CS805 Heated-Needle Anemometer

3. Calibration and System Accuracy

As listed in the previous section, the CS805 has been calibrated and tested in a

controlled environment at 25°C, 646 mmHg (861 mbar, 0.85 atm), and 31.100

mA of constant current. This sensor is going to be exposed to many

applications deviating from the calibration environment, and will continue to

work well. Concerns with calibration and sensor accuracy as the application

environment changes temperature, pressure, and humidity are discussed in

detail in Appendix A. To follow, are the major concerns needing to be dealt

with for proper use, in the order of decreasing error to system accuracy.

3.1 Angular Sensitivity

The CS805 has been calibrated to measure winds in the plane orthogonal to the

axis of the needle. The sensor loses response as the angle between air flow and

axis of the needle decreases. This is quantified with the graph below. The

performance constraints of the CS805 need to be understood in order to make

the desired measurements. If the sensor is not oriented properly upon

installation, it could introduce as much as a 50 percent error into the

measurement. This is further discussed in the installation section.

FIGURE 1. Angular Response of CS805

CS805 Heated-Needle Anemometer

3.2 Pressure Change with Elevation

FIGURE 2. Atmospheric Pressure Change with Elevation

The calibration of the CS805 took place in Logan, Utah, at an elevation of

1.384 km (4500 ft.) above sea level. Unless the sensor is being used at this

elevation, the calibration will need to be adjusted for a pressure change due to

elevation. The heat transport from the needle anemometer is a function of the

fluid passing over the heated cylinder. Thermodynamically, this is a gas, and

the energy transport is being done by mass. The mass and volume of a gas are

directly proportional. As the pressure increases with lower elevations, there

will be more air molecules per volume and more energy transport from the

cylinder. The calibration needs to be adjusted by a ratio of calibration pressure

(Pcalib) to that of the use pressure (Puse). We see this in Equation 1, where u is

wind speed, B is the slope, ∆T is the temperature difference, and A is the

offset.

2/1

use

calib

2/1 P

Au 























∆

+= (Eq. 1)

Atmospheric pressure does not usually change enough from day to day to be

concerned about the effects on the measurement. Experimental validation of

the above theory can be viewed in Appendix A.

3.3 Coupled Error of CE805

The calibration for the CS805 was done with a BK Precision (model 1646)

power supply and a Keithly (model 197A) digital multimeter adjusted to keep

the current 31.1 ±0.005 mA. The CE805 has an accuracy error of 2% over the

full temperature range. It has been bench tested to be within 1% at 25°C.

CS805 Heated-Needle Anemometer

Changes in the current delivered to the CS805 will directly contribute to the

error of the wind speed measurement. When the CS805 is being used with the

CE805 at a temperature different from 25°C the inaccuracy of the current

delivery will alter the measurement. This deviation will show up in the square

root of wind speed domain, and the error will actually double in the wind speed

domain.

For example, if you are operating over a range –20 to 50°C, with the CE805

delivering current to the CS805, that will introduce a 2% inaccuracy in your

current (sqrt (wind speed) domain) and will show up as a 4% inaccuracy in

your wind speed measurement. This would add to the 5% inaccuracy specified

in the CS805.

4. Calibration

As mentioned in the previous section, calibration was done in a controlled

environment at 25°C, 646 mmHg (861mbar, 0.85 atm), and 31.100 mA of

constant current. The calibration is done in a wind tunnel, using Sierra

Instruments’ mass flow meters (700 series) to calculate the wind speed. Each

sensor has been calibrated over the specified range to deliver accurate and

precise measurements within the specifications.

As previously noted, the best fit calibration curve is linear, of the form:

2/1

use

calib

2/1 P

Au 























∆

+= ,

where u is the wind speed, A is the offset, B is the slope, ∆T the temperature

difference, Pcalib the calibration pressure, and Puse is the use pressure, which will

be site specific to the user.

Each sensor comes with a serial number specific calibration giving the user the

slope and offset of the calibrated fit. Pcalib is a function of the elevation in

Logan, Utah, and is: 646 mmHg, 861 mbar, or 0.85 atm, depending upon

preferred units. The calibration is done to output wind speed in cm/s. If the

desired unit is mph, a multiplier of 0.0224 mph/cms-1 needs to be used as the

final adjustment.

For the provided calibration to work in use, the ∆T measurement should be

referenced to an external air temperature measurement. Because of the

datalogger’s thermocouple measurement algorithm, the reference temperature

will need to be subtracted from the original CS805 temperature measurement

to determine ∆T. This is further discussed in the installation and program

example sections of the manual.

5. Installation

The CS805 is most sensitive to wind perpendicular to the axis probe. The

sensitivity deviates as the angle of wind changes from normal, as discussed in

Section 3.1. The probe will also be affected by the free flow of air at the

sensor; any wind shielding by a leaf or building will affect the measurement. It

is suggested to think carefully about the desired measurement and

measurement constraints of the sensor.

CS805 Heated-Needle Anemometer

FIGURE 3. Plane of Calibrated Sensitivity

For example, if the desired measurement were horizontal wind in a desert, the

preferred installation would be to have the probe positioned vertically, the

needles pointing toward the sky. This orientation would provide the greatest

sensitivity to transverse wind. In addition, the contribution of the vertical wind

component to the total wind vector is generally less than the horizontal

components. The probe should be installed free from shrubbery or any nearby

equipment that may inhibit air flow.

Secondly, the differential temperature of the CS805 needs to be referenced to a

separate air temperature measurement. This separate measurement needs to be

made in a vicinity representative of the air temperature at the CS805. This can

be done with any method of temperature measurement, such as a 107 probe or

thermocouple.

Finally, this sensor is fragile and should be treated appropriately. The

protective tip should be used at all times when transporting and installing the

probe. If installed in a rugged environment, such as a plant canopy, care

should be taken to keep leaves from hitting into and damaging the probe. The

CS805 measurement and calibration rely on the needles being kept straight.

Any bending may reduce the sensitivity and damage or break the probe.

CS805 Heated-Needle Anemometer

6. Wiring

FIGURE 4. CS805, Sensor and Wiring Figure

Below is listed the wiring needed for your CS805/CE805/Datalogger system.

The wiring between the CE805 and the Datalogger is not provided by

Campbell Scientific.

CR7, 21 X, CR23X CE805 CS805

H------------------------------------------------------------------------------Green

L ------------------------------------------------------------------------------White

-----------------------------------------------------------------------------Shield

1 -----------------------------------Red

---------------------------------Black

C ---------------------------------------- CTRL

+ 12------------------------------------- +12V

---------------------------------------

CR10(X or T)/CR510 CE805 CS805

HI-----------------------------------------------------------------------------Green

LOW -------------------------------------------------------------------------White

AG----------------------------------------------------------------------------Shield

1 -----------------------------------Red

---------------------------------Black

C ---------------------------------------- CTRL

12 V ------------------------------------ +12V

G ---------------------------------------

Thermocouple + Green

Thermocouple - White

Heater + Red

Heater - Black

Shield - Clear

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